Not sure which level you need to get down to, however: if you want to build packets from scratch, you should start from LoRa and not LoRaWAN. Looking at Seeduino documentation, I would suggest to look at P2P mode (the tx example) (NB: not sure because I do not know this platform, but others have similar LoRa only functionality). You have to build and send the LoRaWAN header, plus your payload. There is some further thing to be careful about (encryption at first, but since you are a cybersecurity student, you know more than me 
).
While maybe even too extreme, this Attiny85 implementation could be of help (because not using LMIC).